Combination photonic time and wavelength division multiplexing method

ABSTRACT

A method is hereby disclosed for a combination photonic time and wavelength division multiplexing method. Parallel digital inputs of quantity “n” are input into “n” modulator loaders for loading into “n” photonic modulators, each having a setup time required to provide a stable modulation state. Subsequently, a photonic pulse of a specified frequency reads the modulation state of each of the “n” photonic modulators. The “n” modulation states may then be processed by “n” delay mechanisms to time the modulation states into a serial multiplexed output comprising a series of synchronizing pulses and data digits. Several parallel digital to serial multiplexers, operating at distinct frequencies, may be used in parallel or in series to comprise a wavelength division multiplexer in accordance with the invention. The present invention also provides an apparatus for interfacing slower electronic components with the higher speed photonic (optical) components by increasing “n,” the number of parallel digital inputs, therefore maximizing the potential capacity of optical transmission. Moreover, the present invention discloses an apparatus to increase the multiplexer efficiency by beginning to load the next set of data into the photonic modulators shortly after previous set has been read and while the previous data set is being delayed and multiplexed into the serial output.

BACKGROUND

[0001] 1. Related Applications

[0002] This application is a continuation of a co-pending patentapplication, Ser. No. 09/075,046, filed on May 8, 1998 and directed to aCombination Photonic Time and Wavelength Division Multiplexer.

[0003] 2. The Field of the Invention

[0004] This invention relates to data multiplexing and, moreparticularly, to novel systems and methods for time and wavelengthdivision multiplexing of binary and non-binary digital information forphotonic transmission and information storage systems.

[0005] 3. The Background Art

[0006] U.S. Pat. No. 5,623,366 to Hait (hereinafter “Hait”), describes aphotonic method of parallel to serial conversion. What Hait does notteach is the apparatus and method of providing the proper pulse timingneeded in FIG. 24A of Hait, when the parallel information input providespulses that arrive in parallel at substantially the same time.

[0007] Hait also does not teach how to use a single pulsed laser system(or other single-pulsed photonic input system) to provide all therequired sequential output pulses, including synchronization pulses,needed to provide a complete serial transmission system.

[0008] Nor does Hait teach how to interface electronic with photoniccomponents to provide serial photonic transmission capable of operatingat a rate faster than the rate at which electronic components provideparallel digital data input.

[0009] In the initial stages of the development of electronic integratedcircuit technology, attempts were made at “pulse racing.” That is,attempts were made to time the delay of signals traveling through acomputer chip so that a number of signals would arrive at a specificlocation having a specific timing relationship determined by the variousdelays applied to each signal. It was found that many of the electronicvariables involved, such as capacitance and inductance, made pulseracing impractical and unreliable as chip frequencies increased.

[0010] Electromagnetic energy, on the other hand, is not affected by thelevel of capacitance and inductance complexities found in computerchips. The amount of delay that occurs along a photonic delay path maybe determined quite accurately even into the sub-picosecond range. Thepresent invention takes advantage of these characteristics ofelectromagnetic energy and the materials used therewith to provide acomplete time-division multiplexing system.

BRIEF SUMMARY AND OBJECTS OF THE INVENTION

[0011] The present invention, a delayed pulse photonic time-divisionmultiplexer, is an apparatus and method of providing parallel digitaldata to serial data conversion having a photonic serial digital outputthat may be used with both binary and non-binary transmissions. A seriesof pulses of photonic energy are input to provide an electromagneticenergy and pulse timing source, which is divided into portions. Aportion of the energy of these pulses is directed into the output toprovide sync (synchronization) pulses that a photonic receiver uses totime the recovery of serial information and convert it into parallelinformation. “In serial” as used hereinafter refers to data in serialformat (i.e., in series).

[0012] A portion of the energy of the input pulses is also directed into“n” photonic modulators, the integer “n” being the number of data digitsthat are to be transmitted in serial within a single data set betweensync pulses. For example, if n=8 and the digits are binary, then a byteof serial information would be sent. If n=32, then a 32-bit word issent. The actual number of digits sent is a matter of engineeringchoice. The engineer may take into account the need for signalamplification within the receiver and/or the transmitter. He may alsoneed to take into account the accumulation of delay error that may occurusing certain types of delay mechanisms.

[0013] The “n” photonic modulators are first set to their datamodulation states, then allowed to complete their setup times, andfinally held in those states while a photonic pulse is directed to eachone. In the case of binary amplitude modulation, the pulses either aretransmitted through each modulator or are inhibited. However, thepresent invention is not limited to binary transmission only, but mayuse multistate semaphore digits that use more than two modulation statesduring each digit time. Thus, the word “digital” in this disclosure mayrefer to either a binary semaphore or one having more than twomodulation states.

[0014] Associated with the group of “n” photonic modulators is a groupof “n” serial timing delay mechanisms. Each modulator has one of thesedelay mechanisms in series with it so that the photonic pulse reads thecondition of the modulator and is delayed sufficiently and directed intothe common output so that the resulting modulated digit arrives at theoutput at its assigned digit time. Therefore, all the “n” modulated anddelayed pulses arrive at the output in serial following a sync pulse andprior to the subsequent sync pulse. This produces a complete data sethaving “n” digit positions filled with the “n” delayed digital pulses.

[0015] Each serial timing delay mechanism may be placed either before orafter its modulator; however, the timing provided by all the delaymechanisms throughout the present invention must be adjusted so as totime the serial digits properly.

[0016] Photonic modulators have a setup time. That is, it takes acertain amount of time for the modulators to stabilize in response totheir controlling electronic inputs. After this setup time has elapsed,the modulators remain stable during the next photonic pulse, which readsthe information loaded into the modulators by the electronic inputs.

[0017] Parallel information is provided through “n” digital informationinputs. Each modulator has associated with it one of “n” modulatorloaders which load digital information from one of the “n” digitalinformation inputs into its modulator. When triggered, the “n” modulatorloaders load the “n” photonic modulators with modulation states from the“n” digital information inputs. To initiate modulator loading and beginthe setup time for the next data set, the input pulses are directed intothe group of “n” modulator loaders.

[0018] The present invention is very versatile, since it may beengineered to match a variety of photonic modulators, parallel inputs,optical transmission lines, and demultiplexers. One reason the presentinvention is superior is that modulators that require a long setup timemay be loaded for the next data set while the previous data set is beingtransmitted. Accordingly, the invention uses time efficiently. As aresult, the present invention may be engineered to accommodate slowmodulators by increasing the number of digit times and the number ofparallel information inputs (that is, by increasing n) without wastingvaluable transmission time and effective bandwidth.

[0019] When photonic parallel inputs are provided along with photonicmodulators and loaders, the setup times may be comparatively short.However, the present invention also has the advantage of being able tointerface very slow electronics with high-speed photonics. In that case,the modulator loaders may be electronic circuits that controloptoelectronic modulators triggered by the photonic pulses using a photodiode. Thus, the complete apparatus for triggering and loading themodulators may involve the use of prior art optoelectronic, electronic,and/or photonic circuitry.

[0020] The loading circuits load information from the digitalinformation inputs into the modulators and hold that information thereuntil the following trigger pulse occurs. The following trigger pulseoccurs after the setup time and the photonic read pulse for that dataset.

[0021] The pulses that trigger modulator loading may require a delaymechanism to prevent a state change within the modulators during thetime that photonic pulses are traveling through the modulators. Thisdepends upon the choice of circuitry. This loading delay mechanism maybe placed between the input pulse source and the modulators. Individualloading delay mechanisms may be inserted as needed to produce properoutput timing before any or all of the “n” photonic modulators.

[0022] A sync timing delay mechanism may also be inserted between theinput pulse source and the output so that sync pulses will be properlytimed in the output. All of these various delay mechanisms may beengineered or made adjustable in order to accommodate a great variety ofhardware components and transmission protocols.

[0023] It should be noted that, in the arrangement having the “n”photonic modulators placed before the “n” serial timing delaymechanisms, the first transmitted data set is not yet set up and loadedinto the modulators from the parallel digital information input untilthe first pulse has read the “n” photonic modulators and/or the syncpulse is not delayed by a full data set time. The result is that thefirst data set following the first sync pulse may be a null data set ormay contain spurious or preset information, depending on the circuitrythat controls the modulators. Some types of receivers require a specificdata set for initialization or calibration. This is one way of providingthe beginning data set.

[0024] The first photonic input pulse triggers the loading of the firstdata set from the parallel digital information input, which will betransmitted following the second photonic sync pulse. Each modulator isloaded while the previous data set is being transmitted. Following thisinitialization, sync pulses are interspersed with data set pulses.

[0025] Wavelength division multiplexing (which may also be referred toas frequency multiplexing) may be accomplished by the present inventionin two different ways. If the parallel input information is alreadywavelength division multiplexed, the present invention may beconstructed using frequency multiplexed logic components and byproviding frequency matched input pulses. Such components are describedin U.S. Pat. No. 5,617,249.

[0026] Wavelength division multiplexing may also be accomplished throughthe combination of multiple multiplexers of the present invention routedinto a common output. If the pulses of the separate wavelengths used arein sync, only one sync pulse need be sent on one of the wavelengths.However, if the pulses of the separate wavelengths used are not in sync,or if the demultiplexer to be used is not capable of providingsynchronization among multiple photonic channels, a sync pulse may beprovided for each wavelength channel using the same method as that bywhich the sync pulses are provided in a single wavelength embodiment.Since each data set-sync pulse data frame may be transmittedasynchronously, the problems associated with wavelength dispersion amongthe wavelength channels may be minimized.

[0027] Because the minimum number for “n” is two, the present inventionmay be described in terms of first and second components. Therefore, thepresent invention is a method of parallel digital data to photonicserial conversion using delayed-pulse timing that may comprise theelements and methods as described in the following paragraphs.

[0028] In certain embodiments, an apparatus in accordance with theinvention may comprise a first photonic pulse input having a firstwavelength, at least first and second digital inputs that constitute afirst parallel digital input, a first multiplexer output, at least firstand second photonic modulators, and at least first and second modulatorloaders for loading the first modulation states into the first andsecond photonic modulators using information from the first paralleldigital input.

[0029] The first and second digital inputs are input to the first andsecond modulator loaders, respectively. Subsequently the modulationstates from the first and second modulator loaders are transmitted tothe first and second modulators where they are converted to photonicdigital pulses for output to the first multiplexer output.

[0030] Similarly, input pulses from the first photonic pulse are inputto the first and second modulator loaders to initiate modulator loadingto the multiplexer output to provide sync pulses, and to the first andsecond photonic modulators to read the first modulation states loadedinto the first and second photonic modulators to provide first photonicdigital pulses of the first wavelength. Moreover, a presently thepreferred embodiment may include a delay mechanism as necessary to timethe arrival of the first photonic digital output pulses at themultiplexer output in serial between the sync pulses.

[0031] The capability of the present invention to load information fromone data set while simultaneously transmitting another data set enablesthe present invention to transmit sequential data frames withoutintroducing undesirable delays between frames. This is accomplishedbecause the delay mechanisms are arranged to provide the photonicdigital pulses at the multiplexer output from a first data set input tothe first parallel data input while the photonic modulators are beingloaded with a second data set from the first parallel digital input.

[0032] A combined wavelength division and time-division multiplexingmethod of the present invention may be produced by providing multiplemultiplexers, as described above, having different photonic wavelengthinputs, and combining the time-division multiplexed outputs from allwavelengths into a common output.

[0033] The method may be implemented by providing a second photonicpulse input having a second wavelength, at least third and fourthdigital inputs that constitute a second parallel digital input, a secondmultiplexer output, at least third and fourth photonic modulators, andat least third and fourth modulator loaders for loading the secondmodulation states into the third and fourth photonic modulators usinginformation from the second parallel digital input.

[0034] The third and fourth digital inputs are input to the third andfourth modulator loaders, respectively. Subsequently the modulationstates from the third and fourth modulator loaders are transmitted tothe third and fourth modulators where they are converted to photonicdigital pulses for output to the second multiplexer output.

[0035] Similarly, input pulses from the second photonic pulse are inputto the third and fourth modulator loaders to initiate modulator loadingto the multiplexer output to provide sync pulses, and to the third andfourth photonic modulators to read the second modulation states loadedinto the third and fourth photonic modulators to provide second photonicdigital pulses of the second wavelength.

[0036] Moreover, one presently preferred embodiment may include a delaymechanism as necessary to time the arrival of the second photonicdigital output pulses at the multiplexer output in serial between thesync pulses.

[0037] Thus, a method of wave division multiplexed time-divisionmultiplexing is made possible by the present invention by combining thefirst and second multiplexer outputs into a single output.

[0038] Photonic modulators may be loaded and controlled in a variety ofdifferent ways. The most common way is electronic. However, severaladditional ways exist, including without limitation mechanical,electromechanical, acoustical, and the like. All of the foregoing wayshave one thing in common: their top switching speeds are much slowerthan the short pulse times that may be achieved with electromagneticenergy, including without limitation laser light. Even these slowmodulator setup times may be accommodated by the present invention.

[0039] For example, if the single digit times (as determined by thelength of the input pulses) are one femtosecond long and anoptoelectronic setup time is one nanosecond, one million serial digitsmay be placed between sync pulses. Transmission parameters may beengineered to account for the properties of whatever components areavailable. One of the advantages of the present invention over otherdevices is that photonic delay mechanisms, including free-flight pathdifferences and/or optical fibers, may be precisely manufactured toprovide the precise timing needed to ensure the reliability of a milliondigits following a single sync pulse. Prior art methods are notsufficiently reliable to make such a transmission protocol practical.

[0040] Another class of photonic modulators are photonically controlled.With such photonically controlled modulators, high-speed parallelphotonic inputs may provide very short setup times. Thus, sync pulserepetition rates, and data transmission rates may be selected to suitthe photonic components being used. Such photonic components may includephotonic transistors, self-exciting electro-optical devices (SEEDS), andnonlinear optical materials.

[0041] The use of photonically-controlled photonic modulators alsoallows for the construction of more complex multiplexers having multipleparallel inputs and various organizations of delay times as needed tomatch the various parallel digital data sources and transmissionprotocols to be used.

[0042] Certain photonic modulators, such as the photonic transistors ofU.S. Pat. No. 5,617,249, may provide frequency multiplexed logic, whichmay be used to frequency 20 multiplex and time-division multiplexinformation simultaneously using the present invention. Each of themultiplexing frequencies must be provided at the photonic input toprovide a series of pulses for each frequency channel. However, withsuitable circuitry, sync pulses need only be sent on one of thechannels. The result is a combination of wave division and time-divisionmultiplexing.

[0043] The present invention may be designed to work with amplitude,phase, spatial and polarization modulation techniques, as needed for aparticular circumstance. Different forms of modulation may be used tomake the separation of sync pulses from data pulses easier at thereceiver and to provide multiple states for the transmission ofsemaphore digits having more than two modulation states. The photonicmodulators, support circuitry and delay mechanisms are selected toprovide the needed modulation combinations. Sync pulses may even bemodulated as multilevel semaphores that may be used for data set routingor other purposes at the receiver. Thus the terms “digit” and “digital,”as used herein include multilevel as well as binary digits.

[0044] The serial output may be used for direct photonic transmissionthrough free space, waveguides, or optical fibers. The output may alsobe directed along a delay path such as a free-space path or an opticalfiber to provide a method of photonic information storage. The outputmay also be written onto or into various information storage mediaincluding holograms, photographs, CD-ROMS, photo-sensitive materials,and the like.

[0045] Even though this disclosure uses optical terminology, the presentinvention may be used with photonic energy anywhere within theelectromagnetic spectrum through the selection of appropriate componentsto match the frequencies being used. Most notable is the microwaveregion, where the present invention may be used to multiplex informationsent via satellite or other microwave links. The recentcommercialization of x-ray technology, including x-ray capillaries (likeoptical fiber for x-rays), may be used to provide multiplexing in thex-ray bands.

[0046] The use of spatial modulation is not common. While spatialmodulation is more complex than the more usual methods, the presentinvention may use this method of transmission. Spatial modulation isparticularly useful when serialization is required inside a photoniccomputer or mass information storage device. Appropriate components maybe used as with the other modulation methods.

[0047] An object of the present invention is to provide an apparatus andmethod of converting parallel digital information input to photonicserial information.

[0048] Another object of the present invention is to provide anapparatus and method for high-speed parallel photonic sampling of presetmodulation states loaded into slow modulators followed by transmissionof the sampled information in serial during the modulator setup time forthe following data frame, thus providing an apparatus and method ofmaximizing photonic throughput by using the shortest transmissiblephotonic pulses, while using slow modulators (even electro-photonicmodulators) having response times longer than the photonic samplingpulses.

[0049] Another object of the present invention is to provide anapparatus and method for optimizing data frame repetition rates bymatching them to the modulator setup times combined with multilevelsemaphores. This may be done to maximize overall transmission rates foreach carrier wavelength and then adding separate carrier wavelengthsuntil a selected transmission medium, be it an optical fiber or afree-space beam, has been saturated to its maximum physicalinformation-carrying capacity.

[0050] Another object of the present invention is to provide anapparatus and method for photonically transmitting electronicinformation using the fastest available electronic and photoniccomponents.

[0051] Another object of the present invention is to provide anapparatus and method for transmitting serial information using digitalsemaphores having more than two modulation states.

[0052] Another object of the present invention is to provide anapparatus and method for transmitting serial information using a varietyof photonic modulation mechanisms and methods.

[0053] Another object of the present invention is to provide anapparatus and method for transmitting serial information into an opticalfiber for the purpose of retrieving the information at a future time.

[0054] Another object of the present invention is to provide anapparatus and method for transmitting serial information to a satellitereflector or transponder, as the present invention may be designed touse photonic energy in the microwave as well as the optical portions ofthe electromagnetic spectrum.

[0055] Another object of the present invention is to provide anapparatus and method for transmitting serial information using thevarious parts of the electromagnetic spectrum including optical (bothvisible and invisible,) microwave, and radio frequencies.

[0056] Another object of the present invention is to provide anapparatus and method for transmitting simultaneous serial(time-division) and wavelength division (frequency multiplexed)information.

[0057] The foregoing objects and benefits of the present invention willbecome clearer through an examination of the drawings, description ofthe drawings, description of the preferred embodiment, and claims thatfollow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The foregoing and other objects and features of the presentinvention will become more fully apparent from the following descriptionand appended claims, taken in conjunction with the accompanyingdrawings. Understanding that these drawings depict only typicalembodiments of the invention and are, therefore, not to be consideredlimiting of its scope, the invention will be described with additionalspecificity and detail through use of the accompanying drawings inwhich:

[0059]FIG. 1 is a schematic block diagram of a parallel digital data tophotonic serial data converter that constitutes the multiplexer of thepresent invention;

[0060]FIG. 2 is a pulse timing diagram illustrating the relationshipbetween photonic pulses and modulator setup times; and

[0061]FIG. 3 is a pulse diagram showing multistate digit time pulses.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0062] It will be readily understood that the components of the presentinvention, as generally described and illustrated in the Figures herein,could be arranged and designed in a wide variety of differentconfigurations. Thus, the following more detailed description of theembodiments of the system and method of the present invention, asrepresented in FIGS. 1 through 3, is not intended to limit the scope ofthe invention, as claimed, but it is merely representative of thepresently preferred embodiments of the invention.

[0063] The presently preferred embodiments of the invention will be bestunderstood by reference to the drawings, wherein like parts aredesignated by like numerals throughout.

[0064] Those of ordinary skill in the art will, of course, appreciatethat various modifications to the details illustrated in the schematicdiagrams of FIGS. 1-3 may easily be made without departing from theessential characteristics of the invention. Thus, the followingdescription is intended only as an example, and simply illustrates onepresently preferred embodiment consistent with the invention as claimedherein.

[0065]FIG. 1 is a block diagram of a delayed-pulse photonictime-division multiplexer which is a parallel digital information tophotonic serial information converter of the present invention. Threedots between components indicate identical components for informationflow lines up through n−1.

[0066]FIG. 2 is a pulse timing diagram that shows how delay times may beorganized for the various required pulses and how they relate to eachother. Three dots within data sets on time line 35 depict identicaldigit times up through n−1.

[0067] The present disclosure is easily understood by examining FIGS. 1and 2 together. Reference characters 1 through 17 are used in FIG. 1 andreference characters 30 through 47 are used in FIG. 2.

[0068] Referring to FIGS. 1 and 2, in the depicted embodiment, a seriesof photonic pulses (optical, microwave, or RF) are provided by photonicsource 1 routed into multiplexer input 2 as shown by time line 30. Theinput pulses 38 a, 45 a, and 40 a are directed through sync delaymechanism 3 to provide sync pulses 38 b, 45 b, and 40 b at photonicoutput 17, as shown in time line 35.

[0069] Certain types of time-division demultiplexers require specializedsync waveforms, such as shortened pulses, or specialized modulationcharacteristics. These may be provided by insertion either with a syncdelay mechanism in line 3 or between photonic source 1 and the othercomponents or both for use in demultiplexing. Electronic digitalinformation may be input to photonic modulators 4, 5, 6 through 7 byparallel digital information input 19.

[0070] Input pulses from multiplexer input 2 as shown on time line 30are also supplied to a group of “n” photonic modulators to sample theirpreviously loaded and held modulation states. Four of the “n” photonicmodulators are shown: photonic modulators 4, 5, 6, and the nth photonicmodulator 7. The output of each photonic modulator is directed into itsown serial timing delay mechanism. Serial timing delay mechanismsdepicted are serial timing delay mechanisms 12, 13, 14 and the n^(th)one 15.

[0071] The integer “n” may be any integer in which at least onemodulator and at least one serial timing delay mechanism are providedfor each digit time in output 17, as shown on time line 35, just as withthose modulator and serial delay mechanism combinations depicted.Examples of output digit times include the first digit pulse 46 and then^(th) digit pulse 47 in example data set 44.

[0072] The output from the group of “n” photonic modulators 4, 5, 6through 7 and the group of “n” serial delay mechanisms 12, 13, 14through 15 is “n” delayed digital pulses that are timed to arrive atoutput 17 in serial. For example, the basic transmission sequence for asingle data frame may begin with a modulator loading sequence initiatedby a timed photonic pulse from photonic source 1 routed to modulatorloaders 8, 9, 10 through 11. In turn, photonic modulators 4, 5, 6,through 7 are loaded during their setup times by modulator loaders 8, 9,10 through 11, with data from parallel digital information input 19. Theloaded modulation states are then held for a period of time to allowphotonic sampling of the loaded modulation states.

[0073] Photonic pulses from photonic source 1 are then routed throughphotonic modulators 4, 5, 6, through 7 to sample their modulationstates. The modulated photonic pulses are then routed and delayed bydelay mechanisms 12, 13, 14 through 15 along with a sync pulse to arriveat output 17 in serial. While the photonic pulses are being routedthrough the delay mechanisms 12, 13, 14 through 15 into the serialoutput 17, the modulators 4, 5, 6 through 7 are once again prepared bymodulator loaders 8, 9, 10 through 11 for data sampling for the nextframe.

[0074] The transmission sequence may be started anywhere in thesequence; however, the information transmitted during the first framemay depend upon several other factors. For example, because photonicmodulators that provide more than two stable modulation states may alsobe used, non-binary semaphores (digits) may be used in the presentinvention. When only two states are used, the digit times are the sameas “bit times,” as commonly used in the electronic serial communicationsart. Digit times shown in FIG. 2 having both top and bottom lines (forexample, as in time line 31) indicate that the actual modulation statesdepend upon the modulation states of the respective modulators.

[0075] While FIG. 2 depicts common amplitude modulation form, the actualform of modulation used may be amplitude, phase, spatial, orpolarization, or any combination of these. The present inventionprovides time-division multiplexing by means of pulse delays regardlessof the modulation method or methods used for the pulses. Certainmodulation combinations may require the use of multiple modulatorsand/or multiple delay mechanisms for each digit time as the engineeringof these components requires. Delay mechanisms may include free-spacedistances, materials having an index of refraction greater than one,waveguides, optical fibers, one-shot multivibrators, and other morecomplex circuitry.

[0076] One advantage of using delaying materials such as glass, opticalfibers, and the like is that these may be machined very precisely tomaintain digit times within tolerance, while allowing or compensatingfor temperature and other fluctuations within the materials being used.Changes that do occur may be accurately measured, and such compensatinginformation may be sent to the demultiplexer in order to compensate atthe receiving end.

[0077] Each of the serial timing delay mechanisms 12, 13, 14 through 15provides a different delay time so that the “n” delayed digital photonicpulses shown on time lines 31, 32, 33 through 34 are combined with thesync pulses at location 16 and arrive at output 17, as 20 shown on timeline 35 as data sets 39, 41, and 44 in serial in between sync pulses. Asan example, the delay mechanisms may comprise optical fibers, theoutputs of which are all directed through a lens and into anotheroptical fiber that comprises output 17.

[0078] The time spaces shown on either side of the sync pulses, such assync pulse 45 b between data set times 41 and 44, are optional and maybe used if needed by a particular demultiplexer.

[0079] Each of the “n” photonic modulators has a required setup timethat elapses before the modulating information in the modulators issufficiently stable to be read by sending a photonic pulse into themodulators. This characteristic, which has often been viewed as adetriment in prior systems, is considered useful in the presentinvention. The summation of digit times that make up a data set, forinstance times 39 or 44, may be designed to be at least as long as oneof the photonic modulator's setup times shown on time line 37. Allmodulator setup times depicted on time line 37 are substantially thesame as, for example, set up time 42.

[0080] If the modulators chosen are very slow in comparison with thephotonics, more digit times may be added to each data set by adding moreparallel inputs in parallel digital information input 19 along withcorresponding modulator loader, photonic modulator, serial timing delaymechanisms, and interconnections. These additions increase the size of“n” until the functional limit of the photonics is reached.

[0081] As an example, if femtosecond pulses, as are commonly produced inthe laser art, are used as the photonic source 1 and photonic modulators4, 5, 6, through 7 having a 2 gHz (0.5 ns) response are used, theparallel digital information input 19 may be expanded to include onehalf-million parallel lines without the use of non-binary digits(semaphores). When non-binary digits are used during each digit time,the information throughput may be greatly multiplied. As a result, thepresent invention may be capable of transmitting 1,000 terabits persecond and beyond using presently available components, whileinterfacing inherently slow electronics to high-speed photonics.

[0082] The length of setup time 42 of photonic modulators 4, 5, 6,through 7 (which depends upon the type of modulators used) and the pulsewidth of the input pulses such as pulse 40 a will determine the maximumpulse repetition rate for the input and sync pulses as shown on timelines 30 and 35, which in turn will determine the number “n”; that is,the number of digit times such as digit time 47 available between syncpulses.

[0083] To initiate modulator loading and the setup times as shown ontime line 37, input pulses from the series of pulses of photonic energyinput at multiplexer input 2 as shown by 110 time line 30 are alsodirected through delay mechanism 18 as shown on time line 36 and into“n” modulator loaders 8, 9, 10 through the n_(th) one here designated11. When electronic components are used, these load triggering pulsesare directed into a photo diode, which starts an electronic modulatorloading circuit as discussed in the summary.

[0084] Each pulse exiting load delay mechanism 18 triggers loading ofthe “n” modulators with new information from parallel digitalinformation input 19, starting the modulator setup time, as for exampletime 42 as shown on time line 37. Pulse setup times as shown on timeline 37 may actually be timed events within the “n” modulator loaders 8,9, 10 through 11 rather than an actual detectable signal having the waveform like that of modulator setup time 42 on time line 37. In view ofthe foregoing, the present invention is as compatible withoptoelectronic modulators and electronic modulator loaders as withphotonic, mechanical, acoustic and other modulating and modulatorloading. As a result, the present invention may provide photonic serialinformation at a speed that is considerably faster than that ofconventional single electronic modulator methods. This advantage isprovided by the use of modulator loading times that occur during thetransmission of the previously loaded and sampled data set. The presentinvention transmits asynchronously, with each sync pulse acting as astart pulse for the data set which follows.

[0085] Input pulses 38 a, 40 a, and 45 a, shown on time line 30, aredirected into the “n” photonic modulators 4, 5, 6, through 7 to readthem. This read time may be at any time that is not simultaneous with asetup time such as 42 shown on time line 37. For example, they may beread during time 43, which is between setup times on time line 37.

[0086] Of particular interest is the relationship between the setuptimes and the first sync pulse in the embodiment shown. The first inputpulse 38 a reads the modulation state of photonic modulators 4, 5, 6,through 7. At that time, the modulators may contain unknown data or maybe off or preset since no setup time has yet occurred. This is becausemodulator read pulses occur before the setup time begins for loading thenext data set. Thus, the first data set 41 may be null or may containunknown or preset data. A null or preset modulation pattern may be usedby certain demultiplexers for determining the source of the informationthat follows, for calibration, or to provide other system information tothe demultiplexer.

[0087] The first parallel digital data set is loaded following pulse 38a, which is delayed by load delay mechanism 18, which in turn triggersthe start of setup time 42. This occurs during the time that the first(possibly null) data set 41 is being transmitted. The photonicmodulators are set up and stable at the completion of setup time 42 sothat they may be read by the second input pulse 45 a.

[0088] The modulator outputs are delayed, each one by an amount thatdiffers by at least one digit time (such as 46 and 47), to theirindividual digit time slots as in time lines 31, 32, 33 through 34 andare combined into output 17 as a complete data set 44, shown in timeline 35. The process then continues in the same cyclic manner for thefollowing trigger, setup, read, delay and transmit sequences.

[0089] The first data set 41 may be eliminated by changing the timingdelays of the various delay mechanisms used throughout the invention. Inparticular, sync delay mechanism 3 may be used to delay the sync pulsesso that the first pulse arrives one data frame later; that is, the firstsync pulse 38 b would then arrive at 45 b. Certain types of delay,modulation, modulator loading, beam combining, and output mechanismsrequire the use of amplifiers and pulse shapers that may be inserted, asneeded within the present invention.

[0090] It should be noted that other embodiments of the presentinvention may place delay mechanisms before the photonic modulatorsand/or sync output while providing other delays before or within themodulator loaders. However, the disclosed embodiment is simple andcompatible with electronic parallel digital information inputmechanisms.

[0091]FIG. 3 shows a non-binary semaphore quadnary digit having fourdifferent amplitude modulated levels 50, 51, 52 through 53, one level ofwhich is transmitted during a digit time (such as digit time 47 of FIG.2) to indicate one of four digits. The parallel digital informationinput 19 may be multi-level, or binary to multi-level encoding may beaccomplished within the modulator loaders 8, 9, 10 through 11.

[0092] There are many combinations of non-binary transmission methodsthat may be used with the “n” photonic modulators. Another example is asshown by waveforms 54, 55, and 56 of FIG. 3, which is ternary. Thesewaveforms indicate the use of a combination of phase and amplitudemodulation. The photonic carrier wave 54 is 180 degrees out of phasewith carrier wave 56 (as indicated by its position below the zero axisline). On the other hand, carrier wave 55 is amplitude-modulated low;this modulation combination is particularly useful wheninterference-based photonic components such as those taught in U.S. Pat.No. 5,093,802 are being used at the receiving demultiplexer.

[0093] If each of the photonic modulators is loaded with non-binarymodulation state combinations, considerably more information may betransmitted during each digit time than if binary modulation is used.Any combination of stable modulation states using any combination ofmodulation methods may be used. The present invention is ideally suitedfor such modulation techniques because the method provides ample timefor loading the modulators, even modulators that are comparatively slow.Multiple modulators may be used for each digit time slot so that thephase, amplitude, polarization, and spatial modulation techniques may bemixed and matched, as the transmitting medium and demultiplexersrequire. Also, the types of delay mechanisms available are compatiblewith a variety of modulation methods.

[0094] The present invention may be used to provide serial photonicinformation for a variety of tasks. The present invention may be usedfor fiber optic transmission, satellite and terrestrial microwave links,and for writing to optical devices such as CD-ROMs, holographic storagedevices, and fiber optic circulating data storage devices.

[0095] The photonic components usable in the present invention includethose having the capability of frequency multiplexing (or wave divisionmultiplexing) so that multiple frequency channels may be usedsimultaneously during each digit time. Such a feature is important whentransmission or information storage mediums such as optical fibers ormicrowave links are combined with repeater amplifiers having a limitednumber of frequency channels available. The present invention may beused with various combinations of frequency channels, pulse repetitionrates, and modulation methods to suit the medium to be driven.

[0096] To accomplish combination wave division and time-divisionmultiplexing, separate carrier wavelengths are routed from photonicsource 1 to separate modulators. For example, red light would be routedto modulators 4 and 5 and green light to modulators 6 and 7.

[0097] The present invention may be embodied in other specific formswithout departing from its structures, methods, or other essentialcharacteristics as broadly described herein and claimed hereinafter. Thedescribed embodiments are to be considered in all respects only asillustrative, and not restrictive. The scope of the invention is,therefore, indicated by the appended claims, rather than by theforegoing description. All changes that come within the meaning andrange of equivalency of the claims are to be embraced within theirscope.

What is claimed and desired to be secured by United States LettersPatent is:
 1. A method for converting parallel data signals to serialphotonic signals, the method comprising: providing a pulse train offirst photonic pulses having a first wavelength and a first pulse;providing a first data signal; providing a first modulator characterizedby a first setup time and a first data status; loading the first datasignal into the first modulator following the first pulse andestablishing the first data status using the first data signal; and thefirst modulator further configured to produce a first data pulse outputin response to a selected pulse of the photonic pulses following thefirst setup time.
 2. The method of claim 1 , further comprising:providing a second data signal; providing a second modulatorcharacterized by a second setup time and a second data status; loadingthe second data signal into the second modulator following the firstpulse and establishing the second data status using the second datasignal; and the second modulator further configured to produce a seconddata pulse output in response to a first selected pulse of the photonicpulses following the second setup time.
 3. The method of claim 2 ,wherein the first and second data pulse outputs occur at differenttimes.
 4. The method of claim 2 , further comprising: delaying the firstdata signal by a first delay time to produce a first delayed signal;delaying the second data signal by a second delay time longer than thefirst delay time, to produce a second delayed signal.
 5. The method ofclaim 4 , wherein the first delay mechanism is adjustable.
 6. The methodof claim 4 , further comprising combining the first and second delayedsignals to provide a multiplexed output.
 7. The method of claim 6 ,further comprising selecting the multiplexed output from the groupconsisting of binary pulses and multi-level semaphores.
 8. The method ofclaim 6 , wherein the first data signal comprises a first datum followedby a second datum, timed such that the second datum is being loaded intothe first modulator while the first datum is being delayed by the firstdelay mechanism.
 9. The method of claim 6 , further comprising:providing a synchronization signal synchronized with the first photonicpulses to provide synchronization to the multiplexed output.
 10. Themethod of claim 9 , wherein the synchronization signal containsinformation for routing the multiplexed output.
 11. The method of claim10 , wherein the synchronization signal is a multi-level semaphore. 12.The method of claim 11 , wherein the multiplexed output containsinformation produced using modulation techniques selected from the groupconsisting of amplitude, phase, spatial, and polarization modulation.13. The method of claim 12 , wherein the modulation techniques are usedto facilitate the separation of the synchronization signal from thefirst delayed signal.
 14. The method of claim 1 , further comprisingselecting the first data signal from the group consisting of a photonicsignal and an electronic signal.
 15. The method of claim 1 , furthercomprising: providing a pulse train of second photonic pulses having asecond wavelength and a second pulse; providing second and third datasignals, respectively; providing a second modulator characterized by asecond setup time and a second data status; providing a third modulatorcharacterized by a third setup time and a third data status; loading thesecond data signal into the second modulator following the second pulseand establishing the second data status using the second data signal;loading the third data signal into the third modulator following thesecond pulse and establishing the third data status using the third datasignal; the second modulator further configured to produce a second datapulse output in response to a second selected pulse of the secondphotonic pulses following the second setup time. the third modulatorfurther configured to produce a third data pulse output in response to athird selected pulse of the second photonic pulses following the thirdsetup time.
 16. The method of claim 15 , wherein the first modulatorfurther comprises a frequency multiplexed logic device.
 17. The methodof claim 15 , further comprising: delaying the first data signal by afirst delay time to produce a first delayed signal; delaying the seconddata signal by a second delay time to produce a second delayed signal;delaying the third data signal by a third delay time longer than thesecond delay time, to produce a third delayed signal.
 18. The method ofclaim 17 , further comprising combining the first, second, and thirddelayed signals to provide a combination time and wave-divisionmultiplexed output.
 19. The method of claim 18 , wherein the combinationtime and wave-division multiplexed output is launched into an opticalfiber having a maximum capacity.
 20. The method of claim 19 , whereinthe combination time and wave-division multiplexed output fills theoptical fiber to its maximum capacity.
 21. The method of claim 18 ,further comprising: providing a synchronization signal synchronized withthe first photonic pulses to provide synchronization to the combinationtime and wave-division multiplexed output.
 22. The method of claim 21 ,wherein the synchronization signal is a multi-level semaphore.
 23. Themethod of claim 21 , wherein the synchronization signal containsinformation for routing the combination time and wave-divisionmultiplexed output.
 24. The method of claim 1 , wherein the modulatorsare photonically controlled.